182 ON DIGITALIC ACID AND THE DIGIT AL ATE S. 
reddish-coloured solution is obtained ; this is to be slowly- 
distilled in a glass retort in order to separate much of the 
water, and care is to be taken that the heat is not too great. 
On cooling, a small quantity of a brown substance decom- 
poses, the clear liquor is to be poured off, and sufficient 
alcohol is to be added to it to precipitate any digitalate of 
barytes which may have escaped decomposition ; by evapo- 
rating the liquor in vacuo, crystals are abundantly formed. 
In all these operations it is requisite to avoid the contact 
of air as much as possible, for the digitalic acid is converted 
by it into a brown substance : notwithstanding the evapo- 
ration in vacuo, the formation of this substance cannot be 
prevented, and the crystals are consequently formed in a 
liquid of a deep colour ; the more the action of the air is 
prevented, the purer are the crystals obtained. The crys- 
tals are to be separated by and pressed between filtering 
paper, dissolved in a small quantity of alcohol, and again 
crystallized in vacuo, by which they are obtained white. 
The properties of digitalic acid thus obtained are, that it 
crystallizes in long needle-form crystals ; it possesses a slight 
peculiar odour, which is increased by heat, and it yields a 
suffocating vapour, a small quantity of which occasions 
coughing ; at a higher temperature it melts, becomes black, 
and burns with a white flame ; it leaves a charcoal which 
readily burns without residue ; no ammonia is produced 
during the decomposition by heat. 
The acid when pure is perfectly white ; but the action of 
light, heat and air upon it is very great, readily converting 
it into a brown product, which colours the solution, and 
from which it is difficult to free it, and on this account the 
greatest care must be taken during its preparation. When 
the acid is dissolved in a small quantity of water, it may 
be converted during evaporation by the water-bath into a 
deep-coloured substance : this is itself acid,insoluble in water, 
slightly soluble in sether, and readily so in alcohol. 
Digitalic acid becomes still more readily brpwn by the 
